1. Field of the Invention
The present invention relates to a toner supply device for use in an image forming apparatus such as a laser printer, etc., for developing an electrostatic latent image by supplying toner to the electrostatic latent image formed on an outer peripheral surface of a photosensitive drum and transferring the image developed on the surface of the photosensitive drum onto a sheet, and particularly to a toner supply device for use in an image forming apparatus, capable of smoothly supplying toner supplied from toner storing part through a toner supply roller to a developing roller without causing clogging with toner in a toner supply path formed around the toner supply roller and the developing roller resulting in obtaining the image with excellent quality for a long period.
2. Description of Related Art
Regarding conventional toner supply devices for use in image forming apparatuses such as laser printers, etc., there have been proposed various types of the devices. In general, such a toner supply device is constructed of a toner storing member including a toner cartridge, a toner supply roller for supplying toner from the toner storing member, and a developing roller for developing an electrostatic latent image on a photosensitive drum by supplying the toner provided from the toner supply roller onto the image. One embodiment of the toner supply device will be explained with reference to FIG. 7. FIG. 7 is an explanatory view showing schematically a main construction of the toner supply device in the prior art.
In FIG. 7, the toner supply device has a toner cartridge 100 which accommodates therein toner and is provided with an opening for toner supply at an almost center in its width direction. This toner cartridge 100 is provided therein with an agitator 103 for agitating toner to supply same into a developing chamber 102 side through a toner supply port 101. A frame F of the developing unit is provided with an opening for toner supply positioned corresponding to the toner supply opening of the toner cartridge 100. Those openings of the toner cartridge 100 and the frame F form the toner supply port 101 in combination with each other.
Below inside the developing chamber 102 constructed of an upper frame F1 and a lower frame F2 of the frame F, a toner supply roller 104 is arranged rotatably in a lower frame F2 side, for supplying the toner supplied through the toner supply port 101 to a developing roller 105.
On an internal wall of the upper frame F1, above the developing roller 105, a blade 107 is fixedly secured with a fixing element 106, whereby regulating a thickness of toner layer formed on the surface of the developing roller 105. This developing roller 105 is also arranged in contact with a photosensitive drum 108. On the peripheral surface of the photosensitive drum 108 is formed an electrostatic latent image by an image exposure device not shown which performs a scanning operation with a laser beam in accordance with image data. The developing roller 105 supplies toner on the electrostatic latent image formed on the peripheral surface of the photosensitive drum 108 to develop the image. The image developed on the surface of the photosensitive drum 108 is then transferred onto a sheet fed from a sheet feeder not shown, forming a resultant image (a visual image) on the sheet.
In the toner supply device in the prior art, meanwhile, a toner supply path 109 indicated by an arrow E in FIG. 7 is formed around the toner supply roller 104 and the developing roller 105, along which the toner supplied from the toner cartridge 100 through the toner supply port 101 is allowed to flow into the developing chamber 102. In detail the toner supply path 109 is formed so as to extend from the toner supply port 101, above the toner supply roller 104, and make a detour along the lower surface of an extruding portion 107A of the blade 107, and finally upward in the developing chamber 102. The extruding portion 107A is formed extruding from a contact portion of the blade 107 in contact with an outer surface of the developing roller 105.
Here, to well supply toner along the toner supply path 109, it is important to make a determination as to the length of the extruding portion 107A of the blade 107, which is the length from the contact portion to the tip end portion of the extruding portion 107A, and also the gap formed between the lower surface of the extruding portion 107A and an outer peripheral surface of the toner supply roller 104. Specifically, if the length of the extruding portion 107A is too long, it allows the toner supply path 109 to make a detour largely toward the developing roller 105, preventing a smooth flow of the toner, and thereby causing clogging in the toner supply path 109 with toner. If the gap between the lower surface of the extruding portion 107A and the toner supply roller 104 is too small, similarly, it prevents the toner from smoothly flowing along the toner supply path 109, causing clogging therein with toner.
Under such a situation, most of conventional toner supply devices are constructed to have the extruding portion 107A determined to 2 mm or more in length and the gap determined to 3 mm or less between the lower surface of the extruding portion 107A and the toner supply roller 104. Accordingly, it is extremely likely to prevent the toner from smoothly flowing on the toner supply path 109 formed around the toner supply roller 104 and the developing roller 105, and thereby cause clogging in the toner supply path 109 with the toner. Due to such the toner clogging, it becomes hard to smoothly supply toner from the toner supply roller to the developing roller, which would prevent the forming for a long time of the resulting image excellent in quality.